[RFC 3927][1] is the specification for how it _should_ be implemented. It has a section [2.1. Link-Local Address Selection][2] which specifies the usage of a RNG and _recommends_ that the RNG should be seeded using the same initial value (e.g. a MAC address) every time. ``` The pseudo-random number generation algorithm MUST be chosen so that different hosts do not generate the same sequence of numbers. If the host has access to persistent information that is different for each host, such as its IEEE 802 MAC address, then the pseudo-random number generator SHOULD be seeded using a value derived from this information. This means that even without using any other persistent storage, a host will usually select the same IPv4 Link-Local address each time it is booted, which can be convenient for debugging and other operational reasons. Seeding the pseudo-random number ``` [1]: https://www.rfc-editor.org/rfc/rfc3927 [2]: https://www.rfc-editor.org/rfc/rfc3927#section-2.1